/*

 * asid.c: ASID management

 * Copyright (c) 2007, Advanced Micro Devices, Inc.

 * Copyright (c) 2009, Citrix Systems, Inc.

 *

 * This program is free software; you can redistribute it and/or modify it

 * under the terms and conditions of the GNU General Public License,

 * version 2, as published by the Free Software Foundation.

 *

 * This program is distributed in the hope it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for

 * more details.

 *

 * You should have received a copy of the GNU General Public License along with

 * this program; If not, see <http://www.gnu.org/licenses/>.

 */

#include <xen/init.h>

#include <xen/lib.h>

#include <xen/sched.h>

#include <xen/smp.h>

#include <xen/percpu.h>

#include <asm/hvm/asid.h>

/* Xen command-line option to enable ASIDs */

static int opt_asid_enabled = 1;

boolean_param("asid", opt_asid_enabled);

/*

 * ASIDs partition the physical TLB.  In the current implementation ASIDs are

 * introduced to reduce the number of TLB flushes.  Each time the guest's

 * virtual address space changes (e.g. due to an INVLPG, MOV-TO-{CR3, CR4}

 * operation), instead of flushing the TLB, a new ASID is assigned.  This

 * reduces the number of TLB flushes to at most 1/#ASIDs.  The biggest

 * advantage is that hot parts of the hypervisor's code and data retain in

 * the TLB.

 *

 * Sketch of the Implementation:

 *

 * ASIDs are a CPU-local resource.  As preemption of ASIDs is not possible,

 * ASIDs are assigned in a round-robin scheme.  To minimize the overhead of

 * ASID invalidation, at the time of a TLB flush,  ASIDs are tagged with a

 * 64-bit generation.  Only on a generation overflow the code needs to

 * invalidate all ASID information stored at the VCPUs with are run on the

 * specific physical processor.  This overflow appears after about 2^80

 * host processor cycles, so we do not optimize this case, but simply disable

 * ASID useage to retain correctness.

 */

/* Per-CPU ASID management. */

struct hvm_asid_data {

   uint64_t core_asid_generation;

   uint32_t next_asid;

   uint32_t max_asid;

   bool_t disabled;

};

static DEFINE_PER_CPU(struct hvm_asid_data, hvm_asid_data);

void hvm_asid_init(int nasids)

{

    static int8_t g_disabled = -1;

    struct hvm_asid_data *data = &this_cpu(hvm_asid_data);

    data->max_asid = nasids - 1;

    data->disabled = !opt_asid_enabled || (nasids <= 1);

    if ( g_disabled != data->disabled )

    {

        printk("HVM: ASIDs %sabled.\n", data->disabled ? "dis" : "en");

        if ( g_disabled < 0 )

            g_disabled = data->disabled;

    }

    /* Zero indicates 'invalid generation', so we start the count at one. */

    data->core_asid_generation = 1;

    /* Zero indicates 'ASIDs disabled', so we start the count at one. */

    data->next_asid = 1;

}

void hvm_asid_flush_vcpu_asid(struct hvm_vcpu_asid *asid)

{

    asid->generation = 0;

}

void hvm_asid_flush_vcpu(struct vcpu *v)

{

    hvm_asid_flush_vcpu_asid(&v->arch.hvm_vcpu.n1asid);

    hvm_asid_flush_vcpu_asid(&vcpu_nestedhvm(v).nv_n2asid);

}

void hvm_asid_flush_core(void)

{

    struct hvm_asid_data *data = &this_cpu(hvm_asid_data);

    if ( data->disabled )

        return;

    if ( likely(++data->core_asid_generation != 0) )

        return;

    /*

     * ASID generations are 64 bit.  Overflow of generations never happens.

     * For safety, we simply disable ASIDs, so correctness is established; it

     * only runs a bit slower.

     */

    printk("HVM: ASID generation overrun. Disabling ASIDs.\n");

    data->disabled = 1;

}

bool_t hvm_asid_handle_vmenter(struct hvm_vcpu_asid *asid)

{

    struct hvm_asid_data *data = &this_cpu(hvm_asid_data);

    /* On erratum #170 systems we must flush the TLB. 

     * Generation overruns are taken here, too. */

    if ( data->disabled )

        goto disabled;

    /* Test if VCPU has valid ASID. */

    if ( asid->generation == data->core_asid_generation )

        return 0;

    /* If there are no free ASIDs, need to go to a new generation */

    if ( unlikely(data->next_asid > data->max_asid) )

    {

        hvm_asid_flush_core();

        data->next_asid = 1;

        if ( data->disabled )

            goto disabled;

    }

    /* Now guaranteed to be a free ASID. */

    asid->asid = data->next_asid++;

    asid->generation = data->core_asid_generation;

    /*

     * When we assign ASID 1, flush all TLB entries as we are starting a new

     * generation, and all old ASID allocations are now stale. 

     */

    return (asid->asid == 1);

 disabled:

    asid->asid = 0;

    return 0;

}

/*

 * Local variables:

 * mode: C

 * c-file-style: "BSD"

 * c-basic-offset: 4

 * tab-width: 4

 * indent-tabs-mode: nil

 * End:

 */